Abstract
The large amounts of organic carbon buried in mangrove wetlands are well recognized, but the lateral dissolved carbon export and greenhouse gas (GHGs) outgassing are often overlooked. In this study, we carried out seasonal observations of dissolved carbon and GHGs in an estuarine mangrove wetland with high input of riverine nitrogen in southeast China in 2019–2020. The results showed that the tidal range and season were the two main factors controlling the lateral dissolved carbon export including total alkalinity (TA), dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). The positive correlations between the average offsets of DIC, TA, DOC and tidal range confirmed the hydrological controls on the exchange of dissolved carbon between the mangrove creek and the estuary. The seasonal variability in temperature, groundwater export and freshwater input resulted in a larger carbon offset during low tidal range in spring and a smaller offset during high tidal range in fall. The mangrove creek acted as a net source of DIC, DOC, TA and GHGs. When the emissions of GHGs were calculated as CO2-equivalents, the average emission of CO2 was four times higher than that of N2O and the average emission of N2O was six times higher than that of CH4. In contrast with pristine mangroves, denitrification in mangrove wetlands with high input of riverine nitrogen played a crucial role in mineralization processes, leading to the production of DIC, TA and N2O. These biogeochemical processes may not be conducive to the blue carbon sequestration in mangrove soils. These findings suggested that there are mutual benefits between the reduced loss of blue carbon and the mitigation of eutrophication when restoring mangrove wetlands and reducing nitrogen pollution.
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The datasets generated during the current study will be available from the corresponding author on reasonable request.
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Acknowledgements
This research was supported by the Key Laboratory of the Coastal and Wetland Ecosystems, and the state Key Laboratory of Marine Environmental Science. We thank Zetao Wu, Mingzhen Zhang for assistance in fieldwork. We thank Xudong Zhu for providing wind speed data recorded by an eddy covariance tower in study site. Special thanks are given to faculty members from the Administrative Bureau of the Zhangjiang Estuary Mangrove National Nature Reserve, Yunxiao, for their support in the research. We are grateful to the editor and two anonymous reviewers for their thoughtful comments.
Funding
This research was funded by the National Natural Science Foundation of China (Grant Nos. 42276171, 41976138, 41907162).
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LZ, WF and CN led the experimental design and approach. LZ, XK, WF, WY and YQ completed with sample collection and data analysis. CP contributed hydrologic data. LZ drafted the manuscript. XK and CN assisted with review and manuscript editing.
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Lu, Z., Wang, F., Xiao, K. et al. Carbon dynamics and greenhouse gas outgassing in an estuarine mangrove wetland with high input of riverine nitrogen. Biogeochemistry 162, 221–235 (2023). https://doi.org/10.1007/s10533-022-00999-5
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DOI: https://doi.org/10.1007/s10533-022-00999-5